Screening apparatus



1951 G. H. STRAIN SCREENING APPARATUS 5 Sheets-Sheet l Filed Aug. 11, 1947 INVENTOR By G. H. STRAIN ATTYS.

Nov. 13, 1951 G. H. STRAIN 2,575,143

SCREENING APPARATUS Filed Aug. 11, 1947 5 Sheets-Sheet 2 F/G. Q.

INVENTOR B RAIN ATTYS.

1951 G. H. STRAIN SCREENING APPARATUS 5 Sheets-Sheet 3 Filed Aug. 11, 1947 lIV|/ENTOR By s. H. STRAIN WW 777 Nov. 13, 1951 G. H. STRAIN 2,575,143

SCREENING APPARATUS I Filed Aug. 11, I947 5 Sheets-Sheet 4 l/VVENTQR 3y G. H. STRAIN ATTVS.

NOV. 13, 1951 STRMN 2,575,143

SCREENING APPARATUS Filed Aug. 11, 1947 5 Sheets-Sheet 5 ammo 3/ G. H. STRAIN +277 A TT VS.

Patented Nov. 13, 1951 UNITED STATES PATENT OFFICE scnuum if isl muus I Q Application August 11, 1947, Serial No. 768,054 InGreat Britain October 16, 1946 Claims. (01. 209- 329) In my prior U. S. Patent No. 2,192,668 I have described a screening device which comprises a rigid member or primary mass to which a reciprocating motion having a vertical component is imparted, and a screen or secondary mass mounted thereon in such manner that it is normally held in contact therewith by the force of a spring or the like, but is free to move against such force away from the position of contact. The upward movement of the screen was abruptly arrested and reversed by collision with an anvil or primary mass from which the screen derived its vibratory motion, the shock of impact being lessened by the interposition of rubber pads between the colliding masses, this produces concussive action.

It has been found in practice that these rubber pads are only partly satisfactory, and according to the present invention they are replaced by springs that determine the deceleration and acceleration of the secondary mass as it approaches and recedes from the primary mass, this producing non-concussive or simple-harmonic motion.

In a convenient arrangement the primary mass divided into a plurality of separate and simultaneously operated units.

The buffer springs may be divided into groups so that they may become operative simultane-' ously or progressively.

The invention is illustrated in the annexed drawings, in which Fig. 1 is a side elevation of a machine of which the screening impulses are perpendicular to the screening surface.

Fig. 2 is a. sectional elevation on the line 2-2 of Fig. 1.

Fig. 3 is a plan.

Fig. 4 is a side elevation of a screening ma chine of which the impulses are inclined to the screening surface.

Fig. 5 is a side elevation of a machine in which the primary mass is divided into two parts.

Fig. 6 is a plan view of a slightly modified arrangement of that shown in Figs. l-3, and

Fig. 7 is a sectional elevation on the line 1--'| of Fig. 6.

Referring first to Figs. 1-3, I is an eccentric driving shaft driven by a shaft la, and 3 is a primary mass driven through the medium of connecting rods 2, the mass 3 being mounted on parallel leaf springs 4. Further springs 5 are located near the centre of the length of side members I of a screening compartment 6, the springs 5 being adjustably secured to the mass 3 by screws,

which enable the springs to be moved into or out of contact with the compartment 6 which has a screening surface 8.

The screening compartment 6 is held in position, relatively to the primary mass 3 by transverse leaf springs 9 which contribute, together with the suspension and buffer springs, to determine the natural frequency of the compartment.

These leaf springs 9 couple the screening compartment to a stationary framework l2, so that the position of the compartment is securely maintained. The compartment is coupled to the primary mass 3 by tension springs lil through which energy from the primary mass is directly transmitted to the compartment 6. The compartment is also coupled to the stationary framework l2 by tension springs H for the purpose of raising or lowering the compartment relatively to the stationary framework. Apart from the leaf springs all the springs are adjustable, and by their arrangement and adjustment, the primary mass leaf springs 4 and the compartment leaf springs 9 may be relieved of load when the machine is at rest. In this condition, the leaf springs are subjected to the least amount of bending stress when the machine is working and, their endurance is enhanced.

When all the buffer springs are at all times .of working in contact with the compartment the motion ofthe latter is simple harmonic in character, and its amplitude is influenced by its natural frequency, which is determined by all the springs in contact with the compartment.

Assuming the primary mass to have a constant amplitude and frequency, the amplitude of the compartment is greater as its natural frequency approximates to that of the primary mass. By reducing or increasing its natural frequency, by using weaker or stronger springs, the compartment amplitude may be reduced to little more than that of the primary mass, and with the proper selection of springs the movement of the compartment may be increased to A2 when vibrating at 1400 per minute. At this speed and movement the compartment has an acceleration much greater than that of gravity so that material being screened is projected clear of the screening surface 8 without the need of impact. By these means, the acceleration of the compartment may be determined to suit the needs of material being screened. If, however, impact characteristics are desired, the springs 5 may be set to part company with the compartment on its down stroke and to meet again on the upstroke, the distance or period of deceleration being determined by the stiffness of the springs.

If the springs are set a little in advance of each other, the process of parting company with the compartment will be progressive and so will be the rejoining, so that deceleration, or impact characteristic, may be usefully varied over a considerable range. V

As the performance of the machine depends upon the ratio of the natural frequency of the secondary mass to the frequency of the primary mass, variation of performance may be achieved by varying the speed of the eccentric driving shaft, the spring setting of the secondary mass remaining constant.

In the arrangement described where the screening impulses are perpendicular to the screening surface it is necessary for the machine to be tilted to cause the material to travel along the surface. I

In the slightly modified arrangementshow n in Fig. 4 the screening impulses -a're"-inclined to the screening surface, the compartment being adapted to function in arr-horizontal position.

' Fig. 5-illustrates anarrangement in which the primary mass is divided-into two halves 3a and fib 'with two sets of leaf springs-4a-ejnd 4b and two sets'oi springs 5a and 5b. The two halves of the mass 3 are driven from a single shaft 5 and compensating links I 3.

In the arrangement shown iriFi'gs. 6 and! the leaf springs c, onwhichthe primary mass 3 is mounted, are repla-ced by coil springs ta-and the mass 3 oscillates in the manner described in Figs. 1+3:

l clain'iz 1. Screening apparatus comprising a, rigid primary mass mounted on springs andsubjected to substantially rectilinear vibrations, asecondary mass comprising ascreening compartment adapted to vibrate in accordance with'the 'movements of said primary mass, buffer-springs interposedbetween the two vibrating masses" and serving to determine the deceleration and ac 'celeration of said secondary mass as it ap screening compartment to a-stationa'ry framework, and transverse springs for holding said screen compartment in position relatively to the primary mass.

2. A non-concussive screening apparatus comprising a rigid primary mass, means for subjecting said primary mass to substantially rectilinear vibrations, a screening compartment constituting a secondary mass adapted to vibrate in accordance with the movements of the primary mass, compressionsprings mounted upon the primary mass and engaging the secondary mass for urging the secondary mass away from the primary mass, tension springs connected to the primary massand the secondary mass for urging the secondary mass towards the primary mass, a stationary framework, and tension springs connected-to said stationary framework and to said secondaryjlmass for urging the secondary mass towards the primary mass.

' 3. A non-concussive screening apparatus as claimed in claim 2 characterized by the fact that transverse springs are-connected to the stationary fr-amework and the secondary mass for holding the secondar'y mass in position relatively to the prir'riary mass; 7

4. A, hon-concussive' screening apparatus as claimed in claim 3 characterized bythe fact that brackets :are mounted on the secondary mass at an angle thereto andthat the-primarymass' is mounted upon'saidbrackets'at'an inclination to said secondary mass and that the longitudinal axes; ofsaid interposed and-tension springs are disposed a'tan-angle tosaid's'econd'ary mass.

5 A non-conc'us'siye screening apparatus as 'claimed inclaim i characterized by the fact that said-primary mass comprises at least two separate and simultaneously operated units. r

GEORGE HARRY STRAIN.

REFERENCES CITED The following references are of record in the file of this "patent:

UNITED STATESPATENTS" Date Number Name Re; 19,817 Wurzbach et a1, r Jan. '7, 1936 2,192,668 Strain -Mar. 5, 1940 2,353,492 OConnor July 11, 1944 FOREIGN PATENTS Number Country V Date 37?;934 Great Britain July '7, 1932 479,366 Great Britain l. Feb. 7, 1938 

